This step differs depending on the frequency of the passive tag produced. For low-frequency (LF) and high-frequency (HF) tags, very thin metal (for example, copper) wire is generally used to produce the antenna. Etched metal (for example, copper or aluminum) is generally used for manufacturing UHF and microwave tag antennas. In these cases, an antenna is also produced by printing it with a conductive ink that contains copper, carbon, or nickel. Different companies may design the tag antenna and the tag microchip.